Yasunori Tominaga

Study on dynamical structure in water and heavy water by low‐frequency Raman spectroscopy

Depolarized Raman spectra below 250 cm−1 in water and heavy water were measured and analyzed from 373 K to the supercooled region. The spectral feature of the central component below 20 cm−1 is stressed in the present work. The spectra below 250 cm−1 in water and heavy water are interpreted as a superposition of one Debye‐type relaxation mode and two damped harmonic oscillators. The damped harmonic oscillators (broadbands around 60 cm−1 and 190 cm−1) are interpreted as the restricted translational modes. Analyzing the temperature dependence of the relaxation mode, the reciprocal relaxation time τ−1 in heavy water changes linearly with τ−1 ∝ (T − 240 K) in the whole temperature range. On the other hand, the temperature dependence of the reciprocal relaxation time in water above 303 K deviates from a straight line which holds below 298 K as τ−1 ∝ (T − 225 K).

Internal modes and local symmetry of PO4 tetrahedrons in KH2PO4 by Raman scattering

Abstract The internal mode Raman spectra of crystalline KH 2 PO 4 (KDP) have been observed above the transition temperature T c , and the local and momentary site symmetry of PO 4 tetrahedrons has been analysed to be C 2 , which is the symmetry of the tetrahedrons below T c . From this result, the mechanism of phase transition in this crystal has been concluded to be of the order-disorder type of distorted PO 4 tetrahedrons. It was a long-pending problem in KDP why the low-lying broad transverse mode (⪅ 150 cm -1 ) appears above T c in the x ( yx ) y spectrum. This has been assigned to the libration mode of the tetrahedrons observed owing to the broken selection rule due to the disordered structure.

Low‐frequency Raman scattering of aqueous solutions of L‐xyloascorbic acid and D‐araboascorbic acid

Depolarized low‐frequency Raman spectra of aqueous solutions of L‐xyloascorbic acid and its epimer D‐araboascorbic acid have been investigated as a function of concentration at 30 °C. The influence of fluorescence in the low‐frequency Raman spectral intensity of D‐araboascorbic acid aqueous solution was removed by the background correction. The reduced χ″(ν) spectrum, which corresponds to the imaginary part of the dynamical susceptibility due to the dynamical structure of water in aqueous solutions, was analyzed with the superposition of one Cole–Cole type relaxation mode and two damped harmonic oscillator modes. The effect of L‐xyloascorbic acid on the dynamical structure of water is less than that of D‐araboascorbic acid.

Collective vibrational modes in molecular assembly of DNA and its application to biological systems. Low frequency Raman spectroscopy

The origin of low frequency modes in a molecular assembly of DNA has been investigated by changing the assembly conditions of DNA molecules. The ∼85 cm−1 broadband in B form DNA was found to be insensitive of the assembly condition, and was ascribed mainly to motions of base pairs bound with hydrogen bonds. The lowest frequency mode was found, on the contrary, to be sensitive to the assembly condition and therefore considered to include motions of backbone chains. Through the observation of the lowest frequency mode in B‐form DNA in biological systems such as lambda phage, chromatin and nucleosome core, we have concluded that from the dynamical point of view the DNA molecules in biological systems is more likely in a solid state than in an aqueous solution state.

Salt-induced volume phase transition of poly(N-isopropylacrylamide) gel

The salt effect on the phase transition of N-isopropylacrylamide (NIPA) gel was studied. The swelling behavior of the NIPA gel strongly depends on the salt concentration and is well described as a function of the chemical potential difference of water molecules in solution from that at the transition. From the analysis of the OH stretching, Raman spectra in water and in various aqueous solutions in terms of collective proton motions reveals that the presence of salts tends to disrupt or distort the water molecules in hydrophobic hydration shell around the NIPA gel. This leads to inducing the growth of the cluster shell around the salts, which leads to gel collapse. The volume phase transitions due to the different types of perturbation (temperature, salt) are induced by the same mechanism, hydrophobic hydration and dehydration, and therefore can be described in a unified manner in terms of the chemical potential and the collective proton motions of water molecules.

Experimental evidence of collective vibrations in DNA double helix (Raman spectroscopy)

The collective vibrational motions in the solid DNA fiber have been found from the wave vector dependence of the low frequency Raman spectra. The main part of the low frequency modes have been assigned to the αxz(αyz) component of the Raman tensor from the polarized Raman spectroscopy.

Coupled dynamics between DNA double helix and hydrated water by low frequency Raman spectroscopy

Low frequency Raman spectra (±50 cm−1) of DNA gels from 0 to −140 °C have been obtained. A drastic spectral change near −20 °C has been observed, and this is well explained by the model of coupled dynamics between the collective vibrational mode of the DNA and the relaxational mode of the secondary hydration shell. The obtained relaxation time of the secondary hydration shell at 0 °C is τ≈4×10−12 s which is the same order as that of bulk water.

Raman spectral of low-lying longitudinal mode of KH2PO4 and KD2PO4 in ferroelectric phase

Abstract The origin of the low-lying modes of KH 2 PO 4 and KD 2 PO 4 in the ferroelectric phase has been clarified by the z(xy)z Raman scattering experiments. The “ S -mode”, which has been usually assigned to the proton tunneling mode in KH 2 PO 4 at T T c , has been found in the z(xy)z spectrum of KD 2 PO 4 in contrast to the x(xy)y spectrum. It has been found that the frequency of the “ S -mode” of KD 2 PO 4 is higher than that of KH 2 PO 4 . These results have shown that the “ S -mode” is far from the proton tunneling mode nor the proton/deuteron mode at all. From the present Raman spectroscopy, it is concluded that the “ S -mode” is assigned to the libration mode of the PO 4 tertahedrons.

Low Frequency Raman Spectra of DNA

The low frequency collective modes of DNA in aqueous solution have been observed by Raman spectroscopy. The broad response at ∼85 cm -1 disappears when DNA is thermally denatured. This fact indicates the existence of characteristic motion of the DNA double helix.

Dynamical structure of water in aqueous electrolyte solutions by low‐frequency Raman scattering

Depolarized low‐frequency Raman spectra of aqueous electrolyte solutions (ACl and BCl2; A=Li, Na, K, Rb and B=Mg, Ca) in the frequency region from −250 to 250 cm−1 have been investigated over a wide concentration range. The spectra were analyzed with one Cole–Cole type relaxation mode and two damped harmonic oscillators. A broad relaxation mode was found below 20 cm−1. For the present aqueous electrolyte solutions, with increasing salt concentration each relaxation time τ becomes longer than that of liquid water τwater. The relaxation time is considered to correspond to the duration time of the tetrahedral structure of bulk water. We have found that the concentration dependence of the ratio τ/τwater is equivalent to the ratio η/ηwater, where η is the viscosity of aqueous solutions.